Stabilization of thermally unstable dmt by certain phosphonic acid derivatives

ABSTRACT

Disclosed is the stabilization of thermally unstable dimethyl terephthalate with a stabilizing quantity of material selected from the group consisting of P-aryl and P-aralkyl substituted phosphonic acids, esters and alkali metal salts.

United States Patent [191 MOI'I et a].

[ June 26, 1973 STABILIZATION 0F THERMALLY UNSTABLE DMT BY CERTAINPHOSPHONIC ACID DERIVATIVES [75] Inventors: Hiroshi Mori; MichioYamamoto;

Koshi Namie, all of Matsuyama, Japan [73] Assignee: Teijin HerculesChemical Company Limited, Tokyo, Japan [22] Filed: Jan. 8, 1971 [21]Appl. No.: 105,070

[52] US. Cl 260/475 B [51] Int. Cl. C07c 69/82 [58] Field of Search260/475 B, 475 PR [56] References Cited UNITED STATES PATENTS 3,461,1538/1969 Tholstrup et a1 260/475 B Primary Examiner-Lorraine A. WeinbergerAssistant Examiner-J5. Jane Skelly AttorneyGeorge H. Hopkins [5 7]ABSTRACT 8 Claims, No Drawings STABILIZATION OF THERMALLY UNSTABLE DMTBY CERTAIN PHOSPIIONIC ACID DERIVATIVES This invention is in thechemical arts. It has to do with that branch of organic chemistrypertaining to alcohol esters of aromatic dicarboxylic acids.

Dimethyl terephthalate (DMT) is a well known normally solid chemical ofcommercial importance. It is used in large quantities in the productionof polyesters from which fibers and the like are made.

Recently, it has become common practice to ship and store DMT in themolten state, that is, at temperatures above 140C. In some instances,however, DMT is unstable to the extent that under such conditions itscolor tends to increase substantially. As a result, the polyester madefrom it is off-color and sometimes has a degree of polymerization lowerthan that which is desired. The problem to which this invention providesa solution is how to stabilize thermally unstable DMT.

In summary, this invention comprises a thermally stable compositionconsisting essentially of thermally unstable DMT and dispersed thereinat a stabilizing concentration material (hereinafter referred to as thestabilizing material) selected from the group of compounds representedby the following general structural formula:

in which R is selected from the group consisting of aryl and aralkyl,and R and R" are selected from the group consisting of H, alkyl, aryland alkali metals. Examples of aryl include phenyl and phenylsubstituted by.at least one substituent selected from the groupconsisting of carboxy, hydroxy and alkyl. Examples of aralkyl includebenzyl and benzyl nuclearly substituted by at least one member of thegroup consisting of carboxy, hydroxy and alkyl. Examples of alkylinclude both straight and branched chain alkyls having one to carbonatoms and preferably one to four carbon atoms, such as methyl, ethyl,propyl, isopropyl, butyl, secbutyl, t-butyl, and the like. The alkalimetals comprise lithium, sodium, potassium, rubidium and cesium.Preferred examples of compounds convered by the formula include:

P-phenyl phosphonic acid sodium P-phenyl phosphonic acid potassiumP-phenyl phosphonic acid diphenyl P-phenyl phosphonic acidP-(p-carboxyphenyl) phosphonic acid diethyl P-benzyl phosphonic aciddiethyl P-[4-hydroxy-3,5-di(t-butyl)benzyl] phosphonic acid and thelike.

Concentration of the stabilizing material in the thermally stabilizedDMT of this invention is in a wide range. However, satisfactory resultsare obtained when the concentration of the stabilizing material issubstantially l-SOO parts by weight per million parts by weight of theDMT.

The composition of this invention is made several ways.

In one procedure it is made by admixing the stabilizing material aloneor with other additives withthe thermally unstable DMT in the moltenstate. This admixing can be performed by adding the stabilizing materialwhile stirring the molten DMT. It also can be done by blowing with aninert gas the stabilizing material into the molten DMT. The resultingmolten composition can be maintained in the molten state until it isused, or it can be cooled until solid.

In another procedure the composition of this invention is made byadmixing the stabilizing material alone or with other additives with thethermally unstable DMT in the finely divided solid state. At the timethe stabilizing material can be in the finely divided solid state, themolten state or dissolved in an inert solvent, which subsequently, ifdesired, is removed by evaporation. Thereafter, when the DMT is meltedfor use, the stabilizing material automatically is incorporated in it.

In still another procedure the composition of this invention is made byadmixing the stabilizing material alone or with other additives with asolution of the thermally unstable DMT in a solvent preferably for boththe DMT and the stabilizing material. Preferably, the stabilizingmaterial when added to the solution is dissolved either in a mutualsolvent or the same solvent. After the stabilizing material has beendispersed in the solution of DMT, the solvent is removed by evaporation,or crystallization of the DMT is effected. In either case the solid DMThas incorporated in it the stabilizing material of this invention.

In yet another procedure the stabilizing material is admixed with moltenDMT so that the concentration of the stabilizing material issubstantially higher than the ultimate use concentration. A stabilizingquantity of the concentrate thus formed is subsequently added to the DMTto be stabilized.

The efficacy of the stabilizing material of this invention instabilizing thermally unstable DMT is demonstrated by the followingtabulated data obtained on sampes of specific embodiments of thethermally stabilized DMT of this invention. The data were obtained bymeasuring the initial color of samples of thermally un- I stable DMTalone and with the indicated additives at the noted concentrations inparts by weight per million parts by weight of DMT. The samples werethen established and maintained at 175C. for 24 hours. The color of eachsample was measured 4 hours and 24 hours after establishing the sampleat 175C.

TABLE Concentration Color (Hazen Units) Additive (ppm) Initial 4 24hr.hr.

None I0 30 100 P-Phenyl phosphonic acid I I0 15 20 IO l0 l0 l5 100 l0 l0l5 Sodium P-phenyl phosphonic acid I IO 15 40 I00 5 l0 I00 5 5 5 None 520 Diphenyl P-phenyl phosphonic acid I 5 l0 60 l0 5 I0 60 I00 5 5 20P-(p-Carboxyphenyl) phosphonic acid 1 5 5 5 10 5 5 S 100 5 5 5 None 5 20Diethyl P-benzyl phosphonic acid I 5 I5 70 The foregoing datademonstrate that the thermally induced increase in coloring of thermallyunstable DMT stabilized according to this invention is substantiallylower than that of thermally unstable DMT without stabilizing material.

Thus, this invention provides a thermally stabilized DMT composition.

A feature of advantage of this invention is that the increase in colorof DMT stabilized according to this invention, which increase is broughtabout by high temperatures at the time of storage or transfer orconversion of it into polyester, is substantially lower than that ofunstabilized thermally unstable DMT. Consequently, polyester made fromDMT stabilized according to this invention has substantially less colorthan polyester made from the thermally unstable DMT without stabilizingmaterial.

Other features, advantages and specific embodiments of this inventionwill become readily apparent to those exercising ordinary skill in theart after reading the foregoing disclosures. In this connection, whilespecific embodiments of this invention have been described inconsiderable detail, variations and modifications of these embodimentscan be effected without departing from the spirit and scope of theinvention as disclosed and claimed.

The language consisting essentially of as used in this specificationexcludes any unrecited substance at a concentration sufficient tosubstantially adversely affect the essential properties andcharacteristics of the composition being defined, while permitting thepresence of one or more unrecited substances at concentrationsinsufficient to substantially adversely affect said essential propertiesand characteristics.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows: i

l. A thermally stable composition consisting essentially of thermallyunstable dimethyl terephthalate and dispersed therein at a stabilizingconcentration material selected from the group of compounds representedby the formula:

O Rll in which R is selected from the group consisting of phenyl, phenylsubstituted by at least one substituent selected from the groupconsisting of carboxy, hydroxy and C C alkyl, benzyl and benzylnuclearly substituted by at least one member of the group consisting ofcarboxy, hydroxy and C C alkyl, and R and R" are selected fromthe groupconsisting of hydrogen, C,C alkyl, phenyl, phenyl substituted by atleast one substituent selected from the group consisting of carboxy,hydroxy and C C alkyl, and alkali metal.

2. A composition according to claim 1 in which the concentration of saidmaterial is 1-500 parts by weight per million parts by weight of saiddimethyl terephthe late.

3. A composition according to claim 2 in which said material consistsessentially of P-phenyl phosphonic acid.

4. A composition according to claim 2 in which said material consistsessentially of sodium P-phenyl phosphonic acid.

5. A composition according to claim 2 in which said material consistsessentially of diphenyl P-phenyl phosphonic acid.

6. A composition according to claim 2 in which said material consistsessentially of P-( p-carboxyphenyl) phosphonic acid.

7. A composition according to claim 2 in which said material consistsessentially of diethyl P-benzyl phosphonic acid.

8. A composition according to claim 2 in which said material consistsessentially of diethyl P-[4-hydroxy- 3,5-di(t-butyl)-benzyl] phosphonicacid.

- UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,742, 025 Dated June 26, 1973 Inventor(s) Morir Y m 8: N mie ('IH-l) Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected, as shown below:

Column 2, line 38, sampes should read samples In the Table, Columns 2, 3and 5 of the first group 10 100 10 100 1 1o 20 y l 10 20 1O l0 15 shouldread l0 l0 15 100 10 1,5 vlOO l0 l0 Signed and sealed this 27thday ofNovember 1973.

SEAL Attest:

EDWARD M.FLETCHER,JR. RENE D. TEGTMEYER Attsting Officer I Actingllommissioner of Patents

2. A composition according to claim 1 in which the concentration of saidmaterial is 1-500 parts by weight per million parts by weight of saiddimethyl terephthelate.
 3. A composition according to claim 2 in whichsaid material consists essentially of P-phenyl phosphonic acid.
 4. Acomposition according to claim 2 in which said material consistsessentially of sodium P-phenyl phosphonic acid.
 5. A compositionaccording to claim 2 in which said material consists essentially ofdiphenyl P-phenyl phosphonic acid.
 6. A composition according to claim 2in which said material consists essentially of P-(p-carboxyphenyl)phosphonic acid.
 7. A composition according to claim 2 in which saidmaterial consists essentially of diethyl P-benzyl phosphonic acid.
 8. Acomposition according to claim 2 in which said material consistsessentially of diethyl P-(4-hydroxy-3,5-di(t-butyl)-benzyl) phosphonicacid.